1. BRD4 is a histone acetyltransferase (HAT) 2. BRD4 HAT activity is distinct in its pattern of acetylation of histone H3 and H4 tails 3. BRD4 acetylates H3K122, a residue critical for nucleosome stability 4. BRD4 histone acetylation results in nucleosome eviction and chromatin de-compaction BRD4 is a chromatin binding protein and transcription factor implicated in many cancers through its regulation of expression of c-myc and other proto-oncogenes. We have shown that BRD4 is a novel histone acetyltransferase (HAT) that regulates chromatin structure and gene expression. They show that BRD4 acetylates H3K122 resulting in nucleosome eviction, chromatin de-compaction and transcriptional activation. BRD4 HAT therefore regulates chromatin structure and gene expression.